#region Copyright & License

//
// Author: Ian Davis <ian.f.davis@gmail.com> Copyright (c) 2007, Ian Davs
//
// Portions of this software were developed for NUnit. See NOTICE.txt for more
// information. 
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
//

#endregion

using System;
using System.Collections;
using Ensurance.MessageWriters;
using Ensurance.Properties;

namespace Ensurance.Constraints
{
    /// <summary>
    /// EmptyConstraint tests a whether a string or collection is empty,
    /// postponing the decision about which test is applied until the type of
    /// the actual argument is known.
    /// </summary>
    public class EmptyConstraint : Constraint
    {
        /// <summary>
        /// Test whether the constraint is satisfied by a given value
        /// </summary>
        /// <param name="actual">The value to be tested</param>
        /// <returns>True for success, false for failure</returns>
        public override bool Matches( object actual )
        {
            Actual = actual;
            string actualString = actual as string;
            ICollection actualColloction = actual as ICollection;
            return actualString != null && string.IsNullOrEmpty( actualString )
                   || actualColloction != null && actualColloction.Count == 0;
        }

        /// <summary>
        /// Write the constraint description to a MessageWriter
        /// </summary>
        /// <param name="writer">The writer on which the description is displayed</param>
        /// <exception cref="ArgumentNullException">if the message writer is null.</exception>
        public override void WriteDescriptionTo( MessageWriter writer )
        {
            if ( writer == null )
            {
                throw new ArgumentNullException( "writer" );
            }
            writer.Write( Resources.Empty );
        }
    }
}